There are numerous apparatus known and employed for separating mixtures of low viscosity materials from high viscosity materials. These methods and apparatus range from simple mechanical squeezing to sophisticated chemical and mechanical techniques.
Generally, the separating technique employed depends upon the type of mixture and the degree of separation desired. One specific mixture requiring separation is a coagulated aqueous emulsion of a polymer which has been prepared by reacting one or more monomers in the presence of an aqueous emulsion. It is desired to separate the coagulant, the polymer, from the aqueous portion, water, so that no more than 8% moisture is present in the coagulant.
Among the numerous techniques employed in the prior art for removing water from a polymer-water mixture is a vertical dewatering screw machine which utilizes an increasing root diameter screw to squeeze the mixture and recover a polymer which contains about 11.5% moisture. However, in order to attempt to reach the 8% residual moisture goal, it is necessary to transfer the polymer from the vertical dewatering screw machine to a second piece of equipment, i.e., a vacuum vented, twin screw extruder.
U.S. Pat. No. 3,859,217 discloses a vertical screw machine for removing water from a coagulant-water slurry. At Col. 6, L. 17, of the aforesaid patent it is stated that the dewatered coagulant is estimated to contain about 10 weight percent water.
U.S. Pat. No. 3,587,450 discloses a horizontal screw machine for continuously removing water from wet elastomer crumb in a first dewatering section and then removing water vapor by heat in a subsequent vaporizing section. It is stated that 5 to 12 percent moisture remains after the first section, and that the remaining water is vaporized and removed as steam in the vaporizing section. In this latter section heat may be supplied, and the frictional heat generated by mechanical working and tearing of the material being dried contributes significantly to the total heat available for the drying action.
The major problems with the aforementioned prior art equipment are (1) the moistures cannot be reduced to the level required, (2) heat must be supplied from an external source to effect the drying action and (3) no vacuum can be applied in the same piece of equipment.